1. Technical Field
The present invention relates to a metamaterial structure, and more particularly, to a metamaterial structure which enables adjacent quantum dots to be efficiently excited.
2. Description of the Related Art
A metamaterial is an artificial material that is able to exhibit desired properties when the unit structure of the material is manipulated.
Recently, many scientists have been researching metamaterials, and particularly in optical fields, attempts have been made to achieve properties such as a negative refractive index, etc. that do not occur in nature, using metamaterials.
As for interactions between light and metamaterials, the size of the unit structure of the metamaterial should be considerably smaller than the wavelength of light. The structures, much smaller than the wavelength of light, interact with electromagnetic waves, and thereby a metamaterial having specific macroscopic properties may be provided. Recently, with the great development of nanoscience, a nanometer-sized material may be designed as desired, making it possible to manufacture a metamaterial which interacts with visible light.
Meanwhile, quantum dots typically have a size ranging from ones to tens of nanometers, and interact with electromagnetic waves having wavelengths as large as tens of times the size of the quantum dots. Quantum confinement caused by the very small quantum dots has an influence on the quantum energy state and thus enables interactions with electromagnetic waves at various wavelengths. Thereby, any type of quantum dots may absorb UV light to thus produce light of different colors in the visible range, depending on the size of the quantum dots.
When quantum dots are excited and thus light is radiated, they are greatly affected by peripheral environments. In particular, in the case where quantum dots are located on a metallic substrate, radiation of light is suppressed due to Purcell effects. Also, in the case where they are placed on a dielectric substrate, radiated light is mostly focused toward the dielectric substrate, making it difficult to actually utilize the produced light.
Upon performing tests using quantum dots and fabricating test devices therefor, quantum dots have to be fixed so as not to move. However, in the case where quantum dots are located on a typical dielectric or metal substrate, as mentioned above, there may be difficulty in efficiently utilizing light emitted from the quantum dots.
A metamaterial typically has a metal hole structure. The important features generated upon interaction with light such as resonance wavelength, etc. are determined by the size and shape of the hole and the materials (a dielectric substrate, etc.) around the metal hole. For example, in the case of a rectangular hole structure, the length of a long side thereof plays a role in determining a resonance wavelength. Typically, at terahertz (THz)-waves or microwaves, the hole structure resonates with the wavelength two times the length of the long side of the rectangular hole.
However, because a metal does not function as an ideal conductor in the visible range, the rectangular hole having a size of tens to hundreds of nanometers resonates with light at a wavelength longer than two times the length of the long side of the rectangular hole. The factor which affects resonance, in addition to the long side of the rectangular hole, is a dielectric substrate which may be located under the metal hole. In this case, resonance red-shifts in proportion to a refractive index of the substrate.
In a structure in which the quantum dots and the hole type metamaterial are combined, when the metamaterial resonates with the wavelength of light which excites quantum dots, external light energy may be efficiently supplied to the quantum dots. On the other hand, when the metamaterial resonates with the wavelength of light excited from the quantum dots, light produced by the quantum dots may be well extracted without suppression of radiation due to Purcell effects. Most typical metamaterials resonate and operate at a single wavelength. However, in the case where the metamaterial may cause resonance at both of two different wavelengths (a wavelength that excites quantum dots and a wavelength of light produced by the quantum dots) at a very local position where quantum dots are placed, this is regarded as a method able to very efficiently utilize the quantum dots.
In a related technique, a metamaterial having negative permittivity and dielectric constant is embodied using SRR (Split Ring Resonator) or double SRR, as disclosed in US Patent Application Publication No. 2010-0067091 (Metamaterials).
The invention disclosed in US Patent Application Publication No. 2010-0067091 (Metamaterials) may accomplish desired properties at a single wavelength.
In another related technique, a dual-band resonant metamaterial operating at terahertz waves using a tunable H-shaped resonator made of gold is disclosed in a treatise [APPLIED PHYSICS LETTERS 93, 191110 (2008)] (title; A dual-resonant terahertz metamaterial based on single-particle electric-field-coupled resonators, Yu Yuan et al.).
The above treatise pertains to a metamaterial operating at terahertz waves, and is independent of quantum dot utilization.